Power supplies for telecommunication equipment, are required to deliver a DC voltage for any type of application. The power supplies are powered by the AC-mains, where the voltage is rectified by means of a bridge rectifier, (other types) etc.
Power factor correction, PFC, circuits are often used in switched mode power supplies and rectifiers connected to the AC-mains. The PFC circuit reduces the harmonic contents in the current drawn from the mains, and controls the power factor to be close to unity. For this purpose, a boost converter is often used; especially at higher power levels.
Y. Zhao, Y. Li, and T. A. Lipo, “Force commutated three level boost type rectifier,” IEEE Industry Applications Society Annual Meeting, pp. 771-777, vol. 2, 199; and J. W. Kolar e H. Ertl, “Status of the techniques of three-phase rectifier systems with low effects on the mains,” IEEE International Telecommunications Energy Conference, p. 16, 1999 describes a three-level boost converter utility interface forming the basis of most three-phase boost converters found in the market today. The utility interface draws nearly sinusoidal current from a three phase utility with a power factor near unity.
U.S. Pat. No. 4,268,899, discloses single phase and three phase embodiments of a rectifier circuit operable as a full wave bridge or as a phase controlled voltage doubler depending on the line-load conditions. The circuit has its greatest power factor at high line conditions.
When high power is being processed, semiconductors like IGBT, MOSFET, diodes, GTO, MCT and others have been the chosen solution for the active switches in the applications found in the industry. However, using those devices has been related with many issues that are limiting the efficiency and/or power density like:                a. Current sharing between paralleled devices        b. Reduction of the switching frequency due to the increased commutation losses which increases the weight and the size of the unit.        
Another drawback of the existing solutions is that the EMI-levels are too high and requires several stages in the input filter in order to reduce both the CM- and DM-noise. This reduces the performance and increases the volume/cost of the unit.
G. V. T. Bascopé e Ivo Barbi, “Generation of a family of non-isolated DC-DC PWM converters using a three-state switching cell”, IEEE 31th Annual Power Electronics Specialists Conference, Volume: 2, pp. 858-863, 18-23 Jun., 2000, incorporated herein by reference, describes the concept of the three-state switching cell, 3SSC.
G. V. Torrico-Bascopé e I. Barbi, “A single phase PFC 3 kW converter using a three-state switching cell”, IEEE 35th Annual Power Electronics Specialists Conference, Volume: 5, pp. 4037-4042, 20-25 Jun., 2004, describes an application of the 3SSC in a single-phase PFC circuit.